The present invention relates to a fuel injector.
German Published Patent Application No. 40 05 455 describes a fuel injector that includes an actuator arranged in an actuator chamber. The actuator chamber is sealed with an actuator seal in the form of a spring membrane with respect to a fuel chamber of the fuel injector into which fuel is added at a high pressure through a fuel inlet. The fuel pressure therefore applies a load on the actuator seal from the side of the fuel chamber, so that a force depending on the cross-sectional area of the actuator seal acts on the actuator.
The fuel injector described in German Published Patent Application No. 40 05 455 has the disadvantage that forces acting on the actuator seal from the fuel pressure are transferred completely to the actuator. In particular when there are pressure fluctuations, uncontrolled mechanical loads are applied to the actuator and can result in destruction of the actuator material and fluctuations in stroke.
Furthermore, when the actuator is actuated against the compressive force of the fuel, a high field energy is stored in the actuator and is dissipated when the actuator is reset, thus causing the actuator to heat up, so that suitable measures are to be taken to prevent overheating of the actuator.
The fuel injector according to the present invention has the advantage over the related art that force-balanced sealing of the actuator is achieved. Therefore, only a low actuator force is sufficient for actuating the fuel injector. In addition, fuel pressure fluctuations are compensated, thus preventing fluctuations in stroke.
It is advantageous that at least one sealing element has an inner metal ring connected to the actuating sleeve and an outer metal ring connected at least indirectly to a valve casing of the fuel injector. This provides a frictional connection which can withstand a high fuel pressure.
The inner metal ring is connected to the actuating sleeve with a peripheral weld in an advantageous manner. Furthermore, it is advantageous that the outer metal ring is connected to the valve casing with a peripheral weld. This permits stable and form-fitting connections that are easy to manufacture and are also resistant to fuel.
It is advantageous that the sealing element has a plastic element connected to the metal rings. This permits simple manufacture of the sealing element, where the sealing element can be adapted to specific uses of the fuel injector through the choice of the plastic element. For example, a large actuator stroke is made possible through the choice of an elastically deformable plastic element with a form-fitting connection.
The plastic element is connected to the metal rings by vulcanization in an advantageous manner. This yields a form-fitting connection of the metal ring to the plastic element which is easy to implement in terms of manufacturing technology.
It is advantageous that at least one sealing element has a membrane. This permits large adjusting motions.
Complete compensation of forces acting on the actuator through the actuating sleeve is achieved in an advantageous manner by way of a difference in cross-sectional areas of the sealing elements. Since the force transmitted from a sealing element to the actuating sleeve is obtained from the product of the fuel pressure multiplied by the cross-sectional area of the sealing element, the transmitted force can be changed by varying the cross-sectional area of the sealing element, while the cross-sectional area of the actuating sleeve remains the same. In this way, a force equilibrium acting on the actuating sleeve can be established.
It is advantageous that the actuating sleeve has a recess which is part of a fuel line leading from a fuel inlet of the fuel injector to the sealing seat. Therefore, the actuator seal also serves as part of a fuel line, thus saving on parts and yielding a more compact fuel injector design.
One end face of the actuator is in contact with a collar of the actuating sleeve in an advantageous manner. It is also advantageous that one end face of the actuator is in contact with a collar of the valve casing. Thus, there is an advantageous transmission of force of the actuator to the valve needle over the actuator seal.